You need a 8MM one.
TORX T-15
Torx #45
Torx T-55. A torque angle meter should be used to install them the correct number of degrees on final tightening. These head bolts are TTY (Torque To Yield) and are actually stretched beyond their elastic limit when installed. New head bolts must be used on reassembly or gasket failures are likely.
Any type of socket can be used to remove a 91' Cavalier wheel cylinder bolt that looks like a reversed torx. However, make sure the socket is a bolt head socket.
Its a torx head T55 not an Allen wrench
torx key t25
the size is E14
I believe it to be a T-55 torx.
The correct size Torx bit is a T-55.
T-55
Found out for myself that it's a Torx E-24.